Electric motor with integrated charger

ABSTRACT

A vehicle includes an electric machine with two sets of galvanically isolated windings, first and second inverters, a switching arrangement, and a controller. During charge, the controller operates the switching arrangement to isolate the first inverter from the electric machine to permit charge current to flow through one of the sets and induce a voltage in the other of the sets. During propulsion, the controller operates the switching arrangement to couple the first inverter with the one of the sets such that the first and second inverters are configured to only power one of the sets.

TECHNICAL FIELD

This disclosure relates to electric drive systems for automotivevehicles, and charging arrangements associated therewith.

BACKGROUND

Hybrid-electric vehicles (HEVs) and battery electric vehicles (BEVs) mayrely on a traction battery to provide power to a traction motor forpropulsion, and a power inverter therebetween to convert direct current(DC) power to alternating current (AC) power. The typical AC tractionmotor is a three-phase motor that may be powered by three sinusoidalsignals each driven with 120 degrees phase separation. Also, manyelectrified vehicles may include a DC-DC converter to convert thevoltage of the traction battery to an operational voltage level of thetraction motor.

SUMMARY

A vehicle has an electric machine including two sets of galvanicallyisolated windings, first and second inverters, a traction battery, and aswitching arrangement. The switching arrangement, during charge,isolates the first inverter from the electric machine such that currentfrom a charge port coupled with a source flows through one of the setsand induces a voltage in the other of the sets to charge the batterywhile isolating the source from the battery.

A vehicle has an electric machine including two sets of galvanicallyisolated windings, first and second inverters each associated with onlyone of the sets, and a controller. The controller, during charge,isolates the first inverter from the electric machine to permit chargecurrent to flow through one of the sets and induce a voltage in theother of the sets, and during propulsion, couples the first inverterwith the one of the sets.

A method for operating a vehicle power system includes responsive tocharge mode, isolating by a controller a first inverter from a first setof windings of an electric machine while a second inverter is coupledwith a second set of windings of the electric machine that aregalvanically isolated from the first set such that current from a chargeport coupled with a source flows through the first set and induces avoltage in the second set to charge a traction battery while isolatingthe source from the traction battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a typical on-board automotive vehiclecharger.

FIG. 2 is a schematic representation of a multi-phase electric machine.

FIG. 3 is a phasor diagram of a multi-phase electric machine.

FIGS. 4a and 4b are schematic representations of effective inductance ofelectric machines.

FIG. 5 is a block diagram of a vehicle with an integrated charger.

FIG. 6 is a schematic representation of an electric drive for asix-phase electric motor.

DETAILED DESCRIPTION

Various embodiments of the present disclosure are described herein.However, the disclosed embodiments are merely exemplary and otherembodiments may take various and alternative forms that are notexplicitly illustrated or described. The figures are not necessarily toscale; some features may be exaggerated or minimized to show details ofparticular components. Therefore, specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a representative basis for teaching one of ordinary skill inthe art to variously employ the present invention. As those of ordinaryskill in the art will understand, various features illustrated anddescribed with reference to any one of the figures may be combined withfeatures illustrated in one or more other figures to produce embodimentsthat are not explicitly illustrated or described. The combinations offeatures illustrated provide representative embodiments for typicalapplications. However, various combinations and modifications of thefeatures consistent with the teachings of this disclosure may be desiredfor particular applications or implementations.

The processes, methods, logic, or strategies disclosed may bedeliverable to and/or implemented by a processing device, controller, orcomputer, which may include any existing programmable electronic controlunit or dedicated electronic control unit. Similarly, the processes,methods, logic, or strategies may be stored as data and instructionsexecutable by a controller or computer in many forms including, but notlimited to, information permanently stored on various types of articlesof manufacture that may include persistent non-writable storage mediasuch as ROM devices, as well as information alterably stored onwriteable storage media such as floppy disks, magnetic tapes, CDs, RAMdevices, and other magnetic and optical media. The processes, methods,logic, or strategies may also be implemented in a software executableobject. Alternatively, they may be embodied in whole or in part usingsuitable hardware components, such as Application Specific IntegratedCircuits (ASICs), Field-Programmable Gate Arrays (FPGAs), statemachines, controllers or other hardware components or devices, or acombination of hardware, software and firmware components.

Despite differences in their architectures, electric vehicles (EVs) havesimilarities in their structures. For instance, a battery, inverter, andelectric motor are typically the main building blocks of any EV. Toenergize the battery and provide power for the motor, two types ofchargers are employed: on-board chargers and off-board (stand-alone)chargers. On-board chargers give flexibility to charge anywhere there isan electric power outlet available. The on-board type has the potentialdrawback of adding weight, volume, and cost to the vehicles. Thus, anypossibility of avoiding the issues of additional charger weight, space,and cost by using available hardware, mainly the electric motor and theinverter, to charger the battery is desirable. Considering the case inEVs, which during charging time the vehicle is not driven and duringdriving time it is not intended to charge the battery pack except forregeneration at braking, the integration of an on-board charger andtraction system seems to be a feasible option.

There are specific requirements for on-board chargers (includinggalvanic isolation) which need to be fulfilled for any integratedsystem. Other aspects to consider regarding integrated chargers arevoltage level adaption, unwanted developed torque in the motor duringcharging, efficiency, low harmonic contents in the current from thegrid, and possible mandatory unity power factor operation.

Due to many advantages that integrated chargers can introduce to thesystem, different types of integrated chargers have been previouslyreported. Most of these integrated chargers however suffered from thelack of galvanic isolation in their structure. Here, certain proposedintegrated charges provide galvanic isolation for the charging process.

Currently, some manufactures do not use integrated chargers and insteadfocus on on-board chargers which do not utilize the electric drivecomponents. FIG. 1 illustrates a vehicle 10 with an on-board chargerarrangement 12 operatively arranged with a power source 14. The on-boardcharger arrangement 12 includes a charging port 16, an electro-magneticinterference (EMI) filter 18, a diode bridge 20, a DC/AC converter 22, atransformer 24, an AC/DC filter 26, a boost converter 28, and a tractionbattery 30. The EMI filter 18 reduces high frequency electronic noisebefore providing input to the diode bridge 20. The transformer 24provides isolation between the DC/AC converter 22 and the AC/DCconverter 26. The boost converter 28 performs power factor correction(and possibly voltage adjustment) to output from the AC/DC converter 26before providing input to traction battery 30.

For high power applications (e.g., electric vehicles), large AC machinessometimes include multiple windings (FIG. 2) fed by multiple inverters.Here, a1 is the inductance of phase a of winding set 1, a2 is theinductance of phase a of winding set 2, b1 is the inductance of phase bof winding set 1, b2 is the inductance of phase b of winding set 2, c1is the inductance of phase c of winding set 1, c2 is the inductance ofphase c of winding set 2, d1 is the inductance of winding set 1 alongthe d-axis, d2 is the inductance of winding set 2 along the d-axis, q1is the inductance of winding set 1 along the q-axis, q2 is theinductance of winding set 2 along the q-axis, and ω is the electricalspeed. The rotor d-axis is at the angle θ₁ relative to the axis of phasea1, and at θ₂ relative to the axis of phase a₂, and α=θ₂−θ₁.

Due to the structure of these multiphase machines, the mutual inductance(magnetic coupling) among groups of phases, in addition to individualphases, is inevitable. This is of interest not only for determiningperformance and designing control systems, but also for analyzing faulttolerance. This cross coupling among the windings (phases) can form atransformer when the energy is injected to only one group of windings.

Under AC steady-state conditions, the RMS values of the d- and q-axisflux-linkages Ψ_(d) and Ψ_(q) can be combined into a phasor:

Ψ_(i)=Ψ_(di)+Ψ_(qi)  (1)

I _(i) =I _(di) +jI _(qi)  (2)

V _(i) =V _(di) +jV _(qi) =R _(i) I _(i) +jωΨ _(i)  (3)

where, i=1, 2 and V_(di)=R_(i) I_(di)−X_(qi) I_(qi)−X_(q1q2)I_(q2) andV_(qi)=E_(qi)+R_(i)I_(qi)+X_(di)I_(di)+X_(d1d2)I_(d2). These equationshave been described graphically in FIG. 3, where Ψ_(di) is the fluxlinkage of winding set i along the d-axis, Ψ_(qi) is the flux linkage ofwinding set i along the q-axis, Ψ_(i) is the total flux linkage ofwinding set i, I_(di) is the current of winding set i along the d-axis,I_(qi) is the current of winding set i along the q-axis, I_(i) is thetotal current of winding set i, V_(di) is the voltage applied to windingset i along the d-axis, V_(qi) is the voltage applied to winding set ialong the q-axis, V_(i) is the total voltage applied to winding set i,Ri is the resistance of winding set i, ω is the electrical speed, E_(q1)is the back electromotive force (EMF) along the q-axis seen by windingset 1, X_(d1) is the reactance of winding set 1 along the d-axis, X_(q1)is the reactance of winding set 1 along the q-axis, X_(d1d2) is themutual reactance of winding sets 1 and 2 along the d-axis, X_(q1q2) isthe mutual reactance of winding sets 1 and 2 along the q-axis, ϕ is theangle between I₁ and V₁, γ is the angle between I₁ and E_(q1), and δ isthe angle between V_(q1) and E_(q1).

The cross-coupling terms appear in the phasor diagram as additionalvoltage-drops, which tend to limit the current. If α=0 (angle betweengroup of phases), there is tightly coupled inductances between the twosets, as already observed; and if these sets are fed from a commonvoltage source, the current in each set will be approximately half thecurrent that would flow in one set if the other were open-circuited.This is a practical point because it implies that in a duplex winding,if one set is open-circuited the current in the other set could increaseby a factor approaching 200%, if it were not regulated. Likewise if oneset is short-circuited, the impedance of the second set will be reducedand its current could also increase to a high value if it is notregulated.

The behavior of the duplex sets is analogous to that of parallelinductances, see FIGS. 4a and 4b , with an equivalent inductance of

$\begin{matrix}\frac{{L_{1}L_{2}} + M^{2}}{L_{1} + L_{2} - {2M}} & (4)\end{matrix}$

In this case if L1=L2=L, then the effective inductance becomes

$\begin{matrix}\frac{L + M}{2} & (5)\end{matrix}$

where Ψ₁ is the flux of coil 1, Ψ₂ is the flux of coil 2, M is themutual inductance of the coils, L₁ is the inductance of coil 1, L₂ isthe inductance of coil 2, and i is the total current. Furthermore, whenα=0, M becomes close to L and the effective equivalent inductancebecomes L. At the same time, the coupling coefficient between the phaseswill be k=1 (theoretically). The total current is that which is limitedby L, and half the current flows in each set. But if one set isopen-circuited, the same total current will tend to flow in one set. Theimplication is that regulation of the current may be helpful.

Since the traction system and on-board charger are not functionalsimultaneously, and considering the acceptable amount of couplingbetween the phases, as discussed above, employing a multiphase electricmachine as a transformer to create isolation for an on-board chargerseems to be a logical approach. FIG. 5 illustrates a high-level proposedarchitecture for an integrated onboard charger and traction system. Inthis example, vehicle 32 includes a transmission 33 and differential 34arranged to directly drive wheel/tire assemblies 36. (Wheel/tireassemblies 37 follow the driven wheel/tire assemblies 36.) The vehicle32 also includes an electric drive system 38 configured to beselectively coupled with the transmission 33 via a clutch 40. Theelectric drive system 38 includes an electric motor 42, an inverter andwindings switching device 44, and a traction battery 46. The inverterand windings switching device 44 is arranged to receive power from anexternal charge cord 48. Power received from the external charge cord 48can be provided to the traction battery 46 via the inverter and windingsswitching device 44 for charging purposes. Similarly, power receivedfrom the traction battery 46 can be provided to the electric motor 42via the inverter and windings switching device 44 to operate theelectric motor 42. A controller 49 (or controllers, used interchangeablyherein) is in communication with and controls the electric drive system38. Of course, other and/or different vehicle configurations are alsocontemplated. Such configurations, for example, need not include thetransmission 33, or clutch 40, etc.

As explained in further detail below, the inverter and windingsswitching device 44 and electric motor 42 perform as the traction systemduring vehicle propulsion, and participate in the charging processduring charging of the traction battery 46.

FIG. 6 shows one proposed topology for the electric drive system 38 ofFIG. 5. In this example, the electric motor 42 includes two sets ofwindings 52, 54, and the inverter and windings switching device 44includes a pair of inverters 56, 58, an inductor bank 60, and switchesS1 through S7. The vehicle 32 also includes an EMI filter 62 and chargeport 64. The charge port 64 is shown coupled with a remote power source66. In traction mode, the controller 49 (FIG. 5) connects the switchesS1, S2, and S3 between the windings 52 and the inverter 56, opens theswitches S5, S6, and S7 to disconnect the inverter 56 from the inductorbank 60, and connects the switch S4 between the traction battery 46 andthe inverter 58 thereby disconnecting the inverter 58 from the inductorbank 60. (In traction mode, the charge port 64 would, of course, not becoupled with the remote power source 66.) In charging mode, thecontroller 49 connects the switches S1, S2, and S3 between the windings52 and the EMI filter 62, closes the switches S5, S6, and S7, andconnects the switch S4 between the inverter 58 and the inductor bank 60to couple the traction battery 46 with the remote power source 66. Thus,in both traction mode and charging mode, the charge port 64 iscompletely isolated from the traction battery 46.

The electric motor 42 is used as a transformer that is connected to thepower source 66 via the EMI filter 62. These components provide theisolation stage. The inverter 58 acts as a rectifier that feeds theDC-DC boost converter, which is formed by the inverter 56 and theinductor bank 60. The DC-DC boost converter provides voltage regulationfor charging and also acts as a power factor correction stage.

Some embodiments may offer certain advantages. The power source can be asingle phase, two phase, or three phase. The primary rectification phaseof the onboard charger can be removed. The DC/AC converter is removed.The electric motor can be used as a transformer. The AC/DC stage isachieved by using an existing inverter. The DC-DC converter is realizedvia an inverter and an inductor bank. The presence of three inductorsand a three-phase inverter can permit an interleaved control strategy,which can further reduce the size and cost of the inductor bank. Theinterleaved control strategy can reduce the stress on the DC-linkcapacitor of the inverter 56. The elimination of the rectification stageand the DC/AC converter can increase the efficiency of the system.

The words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the disclosure andclaims. As previously described, the features of various embodiments maybe combined to form further embodiments that may not be explicitlydescribed or illustrated. While various embodiments may have beendescribed as providing advantages or being preferred over otherembodiments or prior art implementations with respect to one or moredesired characteristics, those of ordinary skill in the art recognizethat one or more features or characteristics may be compromised toachieve desired overall system attributes, which depend on the specificapplication and implementation. These attributes include, but are notlimited to cost, strength, durability, life cycle cost, marketability,appearance, packaging, size, serviceability, weight, manufacturability,ease of assembly, etc. As such, embodiments described as less desirablethan other embodiments or prior art implementations with respect to oneor more characteristics are not outside the scope of the disclosure andmay be desirable for particular applications.

What is claimed is:
 1. A vehicle comprising: an electric machineincluding two sets of galvanically isolated windings; first and secondinverters; a traction battery; and a switching arrangement configuredto, during charge, isolate the first inverter from the electric machinesuch that current from a charge port coupled with a source flows throughone of the sets and induces a voltage in the other of the sets to chargethe battery while isolating the source from the battery.
 2. The vehicleof claim 1, wherein the switching arrangement is further configured to,during propulsion, couple the first inverter with the one of the setswhile isolating the port from the battery.
 3. The vehicle of claim 1,wherein the second inverter is configured to rectify the voltage.
 4. Thevehicle of claim 3 further comprising an inductor bank, wherein theswitching arrangement is further configured to couple the inductor bankwith the first inverter to boost the voltage rectified by the secondinverter.
 5. The vehicle of claim 1, wherein the electric machine is asix-phase electric machine.
 6. A vehicle comprising: an electric machineincluding two sets of galvanically isolated windings; first and secondinverters each associated with only one of the sets; and a controllerconfigured to, during charge, isolate the first inverter from theelectric machine to permit charge current to flow through one of thesets and induce a voltage in the other of the sets, and duringpropulsion, to couple the first inverter with the one of the sets. 7.The vehicle of claim 6, wherein the second inverter is configured torectify the voltage.
 8. The vehicle of claim 7 further comprising aninductor bank, wherein the controller is further configured to couplethe inductor bank with the first inverter to boost the voltage rectifiedby the second inverter.
 9. The vehicle of claim 6, wherein isolating thefirst inverter from the electric machine isolates a traction batteryfrom a charge port coupled with a source of the charge current.
 10. Thevehicle of claim 6, wherein coupling the first inverter with the one ofthe sets isolates a traction battery from a charge port coupled.
 11. Thevehicle of claim 6, wherein the electric machine is a six-phase electricmachine.
 12. A method for operating a vehicle power system comprising:responsive to charge mode, isolating by a controller a first inverterfrom a first set of windings of an electric machine while a secondinverter is coupled with a second set of windings of the electricmachine that are galvanically isolated from the first set such thatcurrent from a charge port coupled with a source flows through the firstset and induces a voltage in the second set to charge a traction batterywhile isolating the charge port from the traction battery.
 13. Themethod of claim 12, further comprising rectifying by the second inverterthe voltage.
 14. The method of claim 13, further comprising boosting byan inductor bank and the first inverter the voltage rectified by thesecond inverter.
 15. The method of claim 12 further comprising,responsive to propulsion mode, coupling by the controller the firstinverter with the first set while the second inverter is coupled withthe second set such that the first and second inverters are configuredto only power one of the first and second sets while isolating thecharge port from the traction battery.